in lane you have a couple jobs:
1) fight over lane brush control so your carry can farm safely: you basically want to get in the brush and pop out all the time, make yourself unpredictable and dangerous by harrassing or just by being a menacing presence because of your kit (read: blitz, alistar). hide in that brush try to get all the free poke you can. sometimes you want to focus one, sometimes the other (say if you're against janna, she'll probably shield the adc so it's better to get hits on her that won't be blocked). if you're against taric, blitz, leona, etc., and they have brush control, just plant a ward in the brush and play safe, bait them into wasting their shit and then counterattack when they're vulnerable
2) give your team map control at bot lane & dragon area: basically you'll want to have wards placed in dragon and tri brush (though if you're blue team you can get away with not warding tri brush if your mid laner wards his right jungle entrance). you'll want to keep that warded as to deterr the enemy jungler and mid from ganking. some junglers gank early and from behind, so if you're against a hecarim or something you might want to ward early. you should also be buying pink wards to set up ganks for your jungler and to give you an advantage if you want to get dragon. try to track their ward placements, so you can think "in 3 minutes that ward will be gone". you can also pink it for the 25g and for overall being an asshole.
3) generate kill opportunities for your carry: basically try to keep trades in your favor by using your abilities to your best benefit (landing both sona Qs, etc.). when you see a kill opportunity ping it and just let your carry deal the finishing blow (though not always
). in lane carries are basically turrets, so it's your responsibility to get them fed. sometimes this takes patience, but do what you can, pink ward the lane brushes so that you can attack them unexpectedly, sometimes you need to flash+ult as with sona to get the drop on them, etc. also try to memorize when their cc is in cooldown so you know the best time to strike. like if you just saw ashe use her ult to save the mid laner or something you know that you have a window to make your move.
4) extend any advantages you have: if you're winning, zone them. if they're dead, get your jungler and a pink on dragon and collect that free cash, if you'd rather take their tower, do so. get wards on their blue buff if you're in the blue team and distract your enemy adc/support while your jungler steals it. all that sort of stuff.
after laning phase it's basically just warding objectives (dragon, baron, buffs), warding important points (jungle entrances, usually placing a ward in the middle of mid lane one of the towers is down) and teamfighting. depending on which support you're playing and the situation you're in, in teamfights you'll want to either initiate (leona, taric, thresh), peel for your carries (lulu, janna), counter initiate (sona, zyra), etc. you'll also want to deny vision by buying tons of pink wards and/or oracles. itemize for cdr and maybe some defenses, depending on what the jungler/top laner got.
that's about it, support is kind of a weird role to play because your effect is not as easily measurable as "dealt 40k damage". it's also pretty tough because you need to know about four different champions and how they mix together. like taric graves was a pretty popular pick since taric could easily set up a graves burst with his stun (plus taric makes graves even more naturally tanky).
and finally don't let trashy adcs give you any shit. sometimes you had to secure a kill because they may die if you didn't, and you're allowed to last hit and even push if your adc went back to base/is dead. you're an adc's babysitter, not his bitch, you carry him through laning phase so he can return the favor late game. you don't owe them shit.
pd: watch this for motivation
http://www.youtube.com/watch?v=Aea9IQlNphU
edit: also know that all ezreals are assholes